The invention relates to a gas spring system for a vehicle.
Such a gas spring system is for example known from German patent document DE 103 36 342 A1. The gas spring system described there has an air spring with a main air chamber to which can be coupled a first additional air chamber and/or a second additional air chamber via a guide system and a valve arranged in the guide system. That is, the main air chamber can be connected to one or two of the additional air chambers in a fluidic manner or can separated from these in a fluidic manner, so that the effective total volume of the air spring, and thereby its spring rigidity, can be changed. The chassis characteristic can be varied in dependence on the effective total volume of the air spring by means of this gas spring system. The lift behavior, the pitch behavior and the roll behavior of the vehicle can be influenced thereby.
One object of the present invention is to provide a gas spring system which optimizes the drive behavior of the vehicle.
This and other objects and advantages are achieved by the gas spring system according to the invention, which includes a multi-chamber gas spring with a main chamber and at least one auxiliary chamber that can be connected to the main chamber, at least on one vehicle axle at the vehicle wheels. A guide value that is dependent on the longitudinal speed and the steering angle of the vehicle serves as basis for calculation of a target rigidity by a control device. The axle rigidity at the vehicle axle equipped with the multi-chamber gas springs is then adjusted corresponding to the target axle rigidity. The guide value, which depends on the steering angle and the longitudinal vehicle speed, precedes in time the actual lateral acceleration of the vehicle. The axle rigidity can thereby be adjusted to the determined target axle rigidity, before the actual lateral acceleration on the vehicle takes effect. This chronological advance serves to adjust the vehicle to the changing actual lateral acceleration already at the time of the steering when passing through a curve and to optimally adapt the drive-dynamic behavior of the vehicle for passing through a curve.
In a first embodiment of the invention, it is further provided that the control device initially changes the spring rigidity of the multi-chamber gas spring, which is arranged on the inner curve side of the vehicle. Which vehicle side represents the inner curve side is determined by the steering angle or the guide value depending on the steering angle. The possibility results thereby to increase the spring rigidity of the multi-chamber gas spring on the inner curve side and the extension of the springs of the multi-chamber gas spring on the inner curve side when turning the vehicle. The curve position and in particular the roll position of the vehicle in the curve is thereby improved considerably.
With a second solution according to the invention, it is suggested additionally or alternatively to adapt the spring rigidities of the multi-chamber gas springs of this vehicle axle in stages in an alternating fashion to the determined target rigidity when adapting the axle rigidity. If for example the axle rigidity is to be increased for adaptation to the target axle rigidity, the spring rigidity of the one multi-chamber gas spring is first increased by one stage, the spring rigidity of the respective other multi-chamber gas spring of this vehicle axle is subsequently increased by one stage. This change in stages in an alternating fashion of the axle rigidity for the adaptation to the target axle rigidity takes place in as many stages as necessary to achieve the target axle rigidity. It has emerged that the change in stages in an alternating fashion of the spring rigidities of the multi-chamber gas springs of a vehicle axle is very comfortable for the vehicle occupants.
Advantageously, a multi-chamber gas spring is associated with each vehicle wheel. The axle rigidities of both vehicle axles can be changed in this manner, whereby an axle load distribution between the front axle and the rear axle can be adjusted in a fixed manner or dependent on parameters.
It is furthermore advantageous if each multi-chamber gas spring has several auxiliary chambers and in particular three auxiliary chambers with gas volumes having different sizes, which can respectively be connected to a respective connection valve via a separate connection channel in a fluidic manner or can be separated from the main chamber in a fluidic manner. The effective gas volume of the multi-chamber gas spring can thus be changed in several stages, so that the spring rigidity of the respective multi-chamber gas spring can also be changed in several switching stages of different size. Due to the fact that a separate connection valve sits in each connection channel, a large degree of freedom is present with the arrangement of the auxiliary chambers and with the arrangement of the connection channels between the auxiliary chambers and the main chamber.
The control device can calculate a guide lateral speed from the longitudinal vehicle speed and the steering angle, which lateral speed serves as a guide value for determining the target axle rigidity. The guide lateral acceleration can be determined in a very simple manner and serves as a measure for the drive-dynamic influence of the vehicle during passing through a curve. The guide lateral acceleration thereby precedes the actual lateral acceleration which effectively acts on the vehicle, so that a chronological advance is achieved when adjusting the axle rigidity.
It is further possible that the control device determines the target axle rigidity on the basis of the guide value with the help of a characteristic field. This is particularly advantageous if the target axle rigidity is determined in addition to the guide value on the basis of at least one further parameter. The target axle rigidity can for example also be determined in dependence on parameters, as vehicle state parameters and/or environmental parameters. The target axle rigidity can be adapted to the respective drive situation in an even more exact manner.
A brake pedal actuation parameter and/or a drive pedal actuation parameter and/or spring paths and/or spring speeds and/or a wheel slip parameter and/or the steering angle speed are for example considered as vehicle state parameters. The mentioned parameters are usually available with modern vehicles and can be transferred to the control device via a vehicle data bus system.
The road surface friction value can be used as an environmental parameter, so that it can be estimated if the determined guide value, in particular the guide lateral acceleration can actually develop due to the road surface friction value which is present. The maximum amount of the guide value can for example be determined in dependence on friction and the guide value can be limited to this maximum amount.
It is further advantageous if the control device compares the longitudinal vehicle speed to a first speed threshold, and, if the longitudinal vehicle speed exceeds the first speed threshold, fixes a minimum front axle rigidity which is larger than the smallest front axle rigidity, and a maximum rear axle rigidity for the rear axle rigidity which is smaller than the largest rear axle rigidity. Due to these limitations of the axle rigidities at the front or rear axle, the drive stability is ensured with longitudinal speeds above the first speed threshold, that is, in particular with very large longitudinal vehicle speeds as they occur for example when driving on the highway.
It is additionally advantageous if the control device compares the longitudinal vehicle speed to a second speed threshold and, if the longitudinal vehicle speed falls below the second speed threshold, fixes a maximum front axle rigidity for the front axle rigidity which is smaller than the largest possible front axle rigidity, and fixes a minimum rear axle rigidity for the rear axle rigidity, which is larger than the smallest rear axle rigidity. The agility of the vehicle can be kept sufficiently high by this measure during steering with longitudinal speeds below the second speed threshold, for example to ensure sufficiently good steerability or maneuverability when driving the vehicle in urban traffic.
The control device can carry out a safety check of the vehicle state and, if a safety-critical drive state is determined by means of the safety check, increase the axle rigidity of the at least one vehicle axle having the multi-chamber gas springs to the maximum possible axle rigidity value. A contribution for increasing the drive safety can thereby be achieved, to keep the vehicle stable, in particular with high lateral accelerations. The control device can compare the steering angle speed with a steering angle speed threshold with a safety check of the vehicle state, and, if the steering angle speed exceeds the steering angle speed threshold, recognize the safety-critical drive state. Such a safety-critical drive state is for example present if the driver initiates an evasion maneuver and thereby changes the steering angle very quickly. By recognizing this critical drive state and the increase of the axle rigidity, the driver is supported and the vehicle is kept as stable as possible with regard to the drive dynamics.
The steering angle speed threshold can thereby be dependent on parameters and in particular be determined in dependence on the longitudinal vehicle speed. With higher longitudinal vehicle speeds, a lower steering angle speed value is already sufficient, in order to conclude a safety-critical drive state, while with low longitudinal vehicle speeds, a larger steering angle speed threshold is established. A critical drive state can thus be determined according to the situation.
The above measures in connection with the safety check can also be carried out independently of the otherwise realized control or regulation of the gas spring system, and thus present an independent design of the gas spring system.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.